Compound electric speaker



1960 SABURO UCHIDA 2,922,849

COMPOUND ELECTRIC SPEAKER Filed Oct. 25, 1956 jg -zis Unite COMPOUND ELECTRIC SPEAKER Saburo Uchida, Bunkyo-Ku, Tokyo-To, Japan, assignor to Fukuin Denki Kabushiki Kaisha (known as Fukuin Electric Works, Ltd.), Tokyo-To, Japan, a Japanese limited-liability company This invention relates to speakers and more particularly to an improved compound electric speaker.

In any electric speaker utilizing a single oscillation cone, a certain broadening of the sound reproducing band is to be expected. However, the resulting intermodulation of the various frequencies contained in the reproduction band damages the quality of the reproduced sound. For the purpose of preventing the inter-modulation and of improving the frequency character, there has been proposed a compound electric speaker having two or more combined oscillation parts which are adapted to both highand low-pitch sounds. There are two types of electric speakers, in which oscillation cones of small diameter are attached to either a single main oscillation cone or to a moving coil. The former is very complicated in its construction while the latter is very inferior in its characteristics though its construction is simple.

A principal object and feature of this invention is to provide an improved compound electric speaker having none of the above-mentioned disadvantages.

Other objects of this invention are accomplished by exciting the oscillation, cones adapted to the high and low frequency bands, by means of moving coils which are arranged in a single magnetic field.

The novel features of my invention are set forth in detail in the appended claim. The invention itself, however, both as to its organization, construction, and operation, together with further objects and advantages, may be understood best with the aid of the following description and accompanying drawing, in which:

Fig. 1 is a vertically sectioned side view of a speaker of this invention.

Fig. 2 is an enlarged side view of a part of the speaker illustrated in Fig. 1.

In Figs. 1 and 2, the electric speaker includes a permanent magnet 1, a center magnetic pole 2 and an iron yoke 3. Two end poles 3a of the yoke face the center magnetic pole 2 and are spaced therefrom by a small ringshaped air gap G.

A moving coil 4 is oscillatably supported in the air gap G and is adapted to low-pitch sound by means of a center supporting damper 11. The coil being supported by an oscillation cone 6 adapted to low-pitch sound. The cone 6 is oscillated by oscillation of the coil 4. Another moving coil 5, adapted to high-pitch sound, is supported by a greasy layer 15 adhering to the surface of the center magnetic pole 2 in the air gap G so as to face the moving coil 4 through an air gap. This coil is connected to an oscillation cone 7 which is adapted to high-pitch sound so as to make said cone oscillate.

The cone 7 is supported at its upper opening periphery by a supporter 10 which in turn is attached to a center rod 8 by a nut 9, the rod being screwed in the center pole 2. The illustrated speaker is provided with a frame 12, a packing ring 13 supporting the oscillation cone 6, and a center guide 14 supporting the center magnetic pole 2.

It will be seen from the above-mentioned description States Patent 0 2,922,849 Patented Jan. 26, 1960 that it is possible to obtain a simple and effective compound electric speaker having no variation of tone quality, said variation being caused by inter-modulation, by dividing the oscillation system into two independent oscillation systems, the one being adapted to high-pitch sound and the other to low-pitch sound.

In an oscillation cone adapted to high-pitch sound, oscillation is generally divided into various divisional oscillations whose amplitudes are negligibly small. The divisional oscillations cause occasional side-oscillations. These can be effectively eliminated when the moving coil, adapted to high-pitch sound, is supported on the outside surface of the center magnetic pole by a layer made of a greasy material such as silicon resin grease. In this manner, side-oscillations occurring in the high frequency band will be efiectively damped, making the response characteristic of the speaker for the higher frequency band highly favourable.

The reproduction limit of a low-pitch sound in any oscillation cone adapted to low-pitch sound is about 2000 cycles. This limit varies with the diameter and design of the cone while the output energy of the amplifier is applied mainly to the moving coil which is adapted to low-pitch sound. Only weak current from a divided circuit is applied to the moving coil adapted to high-pitch sound, so that a very thin wire may be used for the moving coil, resulting in a narrower magnetic air gap.

Thus, two kinds of moving coils, can be effectively operated in a magnetic field of strong intensity using less of an air gap than has heretofore been possible.

I have shown a particular embodiment of my invention and described a particular method of its operation, but I do not wish to be limited to this description, since modifications may be made. The appended claim will cover such modifications as may fall within the true spirit and scope of my invention.

I claim as my invention:

An electrodynamic acoustic apparatus comprising a high-frequency first oscillation cone, a high-frequency first coil for receiving audio-frequency currents of relatively high frequencies connected to said first cone to drive the first cone in response to said audio-frequency currents to generate high pitch sound-pressure waves, a low-frequency second oscillation cone mounted substantially coaxially with the first cone and spaced radially therefrom, a low-frequency second voice coil electrically independent of the first voice coil for receiving audiofrequency current of lower frequencies than the currents received by the first coil, said second voice coil being mounted on the second cone to drive the second cone in response to said lower audio-frequency currents to generate low pitch sound-pressure waves, means comprising magnetic means defining an air gap for generating a magnetic field common to said two voice coils, said magnetic means comprising a magnetic pole member disposed axially of the first voice coil for supporting said first voice coil, a silicon-resin grease material between the pole member and the first voice coil to allow the pole member and the voice coil to move relative each other in a direction axially of the pole member.

References Cited in the file of this patent UNITED STATES PATENTS 1,676,668 Round July 10, 1928 2,007,749 Anderson July 9, 1935 2,235,654 Steers Mar. 18, 1941 2,269,284 Olson Jan. 6, 1942 FOREIGN PATENTS 29,279 France Mar. 17, 1925 (1st add. to 574,642) 

